Belt drive systems are frequently used, particularly for driving auxiliary units associated to an internal combustion engine. For providing a tension in the belt of such a belt drive system, a tensioning roller acts onto the belt. The tensioning roller is under the action of biasing spring means. For damping the tensioning roller movement, a damper unit is provided. In many cases, the tension of the drive belt is dependent on the running direction of the drive belt. In a first or normal driving direction, the belt tension is sufficient for maintaining the belt in driving engagement with respective belt pulleys. If the driving direction is reversed, a reduction of the belt tension occurs, and this reduced tension may result in a disengagement of the belt and the respective pulleys. Normal damping of the tensioning roller cannot prevent this disengagement of the belt and the belt pulleys if a reversal of the driving direction occurs.
A reversal of the driving direction is particularly to be expected with internal combustion engines, and more particularly with diesel engines, when the operation is interrupted.